Former US President Donald Trump has been charged with plotting to overturn his 2020 election defeat. He is accused of four counts including conspiracy to defraud the US, tampering with a witness and conspiracy against the rights of citizens. The indictment caps an inquiry into events surrounding the 6 January 2021 riot at the US Capitol. Trump, 77, who is again running for president, denies wrongdoing. On social media he called the case "ridiculous". The Republican politician has already been charged in two other cases: with mishandling classified files and falsifying business records to cover up a hush-money payment to a porn star. The election investigation has focused on Trump"s actions in the two-month period between his loss to Joe Biden and the riot in Washington DC, where his supporters stormed Congress as lawmakers certified the Democrat"s victory. The man leading the inquiry, special counsel Jack Smith, said: "The attack on our nation"s capital on January 6 2021 was an unprecedented assault on the seat of American democracy. "As described in the indictment it was fuelled by lies." Smith wrapped up his brief statement by pledging to seek "a speedy trial", while emphasising that the former president "must be assumed innocent until proven guilty". Trump is due to appear in court on Thursday in Washington DC. The 45-page indictment lists six unnamed co-conspirators: four lawyers, a justice department official and a political consultant. The court document accuses Trump of a "conspiracy to impair, obstruct, and defeat the federal government function through dishonesty, fraud and deceit". Addressing Trump"s allegations of voter fraud in 2020, prosecutors say: "These claims were false and the defendant knew that they were false." They also say Trump tried and failed to convince Vice-President Mike Pence to attempt to block Biden"s certification as president on January 6, 2021. "As violence ensued, the Defendant and co-conspirators exploited the disruption by redoubling efforts to levy false claims of election fraud and convince members of Congress to further delay the certification based on those claims." The indictment also lists the numerous US officials and senior Trump campaign workers who, it says, informed the outgoing president that he had lost and that there was no evidence of voter fraud. Trump, who now faces 78 criminal counts overall in three different cases, is currently the frontrunner in the Republican Party"s contest to pick its next presidential candidate. Whoever wins will challenge the Democratic nominee, expected to be President Biden, in November 2024. The Trump campaign said in a statement that Tuesday"s indictment amounted to election interference. "The lawlessness of these persecutions of President Trump and his supporters is reminiscent of Nazi Germany in the 1930s, the former Soviet Union, and other authoritarian, dictatorial regimes," said the campaign. It added: "These un-American witch hunts will fail." Dozens of top Trump administration officials and advisers were interviewed as part of the investigation, including Pence and former Trump lawyer Rudy Giuliani. Prosecutors in the state of Georgia are also investigating the former president on similar grounds, focusing on whether he illegally pressured officials there to discard Biden"s poll victory. A decision by prosecutors in Atlanta on whether to indict Trump is expected this month. Republicans in other states are being investigated for allegedly helping Trump"s push to stop Biden from taking office. State prosecutors in Michigan charged a former Republican attorney general candidate and another Trump supporter with tampering with voting machines in an effort to prove that Mr Trump had lost due to widespread voter fraud. The riot at Congress led to Trump"s second impeachment in the House of Representatives -- making him the first US president ever to be impeached twice. — BBC